Literally, obesity means a condition characterized by excessive body fat. But one might question: "How much body fat can be called excessive? How do I know I'm overweight?" 

There are many factors that help us determine whether or not someone is overweight. Bone density, muscle mass and other considerations may create such wide variations that if two people weigh the same, one may be overweight and the other may not. 

There have been different methods to determine whether or not one is overweight. But when using one of these methods, you should always keep in mind that it is body fat that really counts. New clinical guidelines use three key measures, namely: body mass index (BMI) (a measure of body fat); waist circumference; and a patient's risk factors for diseases and conditions associated with obesity, such as hypertension and diabetes. 

Body mass index (BMI) is a figure derived by multiplying a person's weight (pounds) by 703 and then dividing it twice by the height (inches). A BMI below 20 is considered underweight, 20 to 24.9 normal, 25 to 27.9 mild obesity, 28 to 34.9 medium obesity, 35 to 39.9 severe obesity and a figure of 40 or greater is considered morbid obesity. These figures are especially important to those who are at risk for diseases such as heart diseases and diabetes. 

Waist circumference reflects the amount of abdominal fat, an important indicator of one's risk of disease. Studies show that with increased waist circumference there is also an increased risk for heart diseases, diabetes and impaired functioning.